For a great many years it has been common practice to build pianos with vibratory strings which are hit by hammers forming part of piano actions actuated by the piano keys. Each action has been so constructed that a hammer is started in motion towards its string or strings upon depression of a key. The key and the mechanisms interconnecting the key and the hammer move to a limit position at which the hammer is no longer moved by the key and interconnecting mechanism, but continues solely by virtue of its own inertia into percussive engagement with the respective string or strings, and then rebounds to a rest position. Pianists are used to the feel of the action, particularly the "let-off" at which the hammer is no longer propelled by the key and interconnecting mechanisms, but continues in motion by virtue of its own inertia.
Various efforts have been made heretofore to construct electronic pianos. The most successful of these have utilized a modified piano action in which a hammer is impulsed into percussive engagement with a vibratory member of some sort, for example, a reed, the vibration of which is sensed by means of electrostatic capacitance, or by a magnetic sensor. Such pianos have been portable, but are rather heavy for true portability. In addition, the sound produced thereby has well approximated a piano tone, but has been distinguishable therefrom, particularly in the lower half of the keyboard, due to the different harmonic structure of vibrating strings and other vibratory bodies, such as reeds.
With the advent of modern electronics, in particularly large scale integrated circuits, it has been possible to simulate the sound of a conventional string piano with remarkably realistic sound. A preferred example of a satisfactory circuit for electronic piano tone simulation is to be found in the copending application of William R. Hoskinson, Ser. No. 037,687, filed May 10, 1979, for "Tri-State Encoding Circuit for Electronic Musical Instrument", assigned to the same assignee as the present application. The Wurlitzer Company of DeKalb, Ill.
Electronic tone generators for electronic pianos have been satisfactory in producing desired piano tones. However, pianists have not been satisfied with the touch or feel, since electronic tone generation is effected by movement of a simple switch contact from a rest position to an active position.
Efforts have been made in the past to simulate the feel or touch of a conventional piano without incorporating a hammer which is operative to strike a vibratory member for producing oscillations to effect generation of a piano tone. The patent art discloses moving mechanisms, including movable electromagnetic transducers for effecting electrical switching and simultaneously providing somewhat of a piano feel. There are several such U.S. patents in the name of Dijksterhuis, U.S. Pat. No. 3,231,661 and the reissue thereof, U.S. Pat. No. Re. 27,015 being exemplary.
There is additional patent art relative to piano practice keyboards in which springs and shaped stop devices have been utilized in an effort to produce a piano-like feel, see for example Stein U.S. Pat. No. 2,684,006. Further efforts have been made to utilize interacting lever devices which are supposed to produce a piano-like feel, see for example Murakami U.S. Pat. No. 4,091,702.
To the best of the present applicants' knowledge none of the foregoing or any other electronic pianos have come into commercial use which have electronically generated piano-like tones and have provided the feel or touch of a conventional piano action.